In the control of production machines, especially spinning machines, the control operations are complicated by the large number of effectors and sensors which are provided. For example, during the operation of a spinning machine, frequently several hundred working stations must be monitored for development of yarn breaks or sluggish spindles, i.e. spindles whose speeds fall below the set point or limiting speed by an impermissible amount. If a yarn break at a certain work station is detected, this station is preferably brought to standstill and further feed of the material to be processed, e.g. a roving or sliver, must be prevented, e.g. by the activation of a roving-stop device.
In spinning machines of a significant length, the cabling between the sensors and effectors at the work stations and the central control station usually located at an end of the machine, contributes an especially high cost to the overall capital cost of the machine.
To reduce the cabling cost, it has been proposed, for example, in German patent document DE 38 13 945, that the sensors and effectors of a machine segment be connected by means of channels which collect the data flow. Data concentrators are provided for communication with the central unit and the data concentrators can be connected by a bus system.
A drawback of this control system for a spinning machine is that, with enlargement of the machine to add, for example, additional spindles or working stations, a higher data transfer rate is required and, unless the bus has been overdesigned to accommodate the higher data transfer rate, the bus system may limit the expansion of the machine.
EP 0 389 849 A2 describes a control system for a textile machine in which each production station is provided with a local electronic circuit which is designed for autonomous control of that station at least in part so that it assumes at least a portion of the control function. A plurality of such production stations form a section of the textile machine and each such section can have a control circuit to which the local control is subordinated. All of the section control circuits can be connected via a data bus to the central machine control unit which has still a higher level in the control hierarchy.
In this manner a largely decentralized control system is provided and the data bus need handle only a limited amount of data. The disadvantage of such a system, however, is that the local circuit at the particular production station must be designed for, and have the capacity for, a multiplicity of important control functions or all of the important local functions. This circuitry, therefore, can be very complex and must be designed individually for each production station so that expansion of machine functions or control functions or even of the machine itself is complicated.